Computer security is fast becoming an important issue. With the proliferation of computers and computer networks into all aspects of business and daily life--financial, medical, education, government, and communications--the concern over secure file access is growing. A common method of providing security is using passwords. Password protection and/or combination type locks are employed for computer network security, automatic teller machines, telephone banking, calling cards, telephone answering services, houses, and safes. These systems generally require the knowledge of an entry code that has been selected by a user or has been preset.
Preset codes are often forgotten, as users have no reliable method of remembering them, Writing down the codes and storing them in close proximity to the access control device (i.e. the combination lock) results in a secure access control system with a very insecure code. Alternatively, the nuisance of trying several code variations renders the access control system more of a problem than a solution.
Password systems are known to suffer from other disadvantages. Usually, a user specifies a password. Most users, being unsophisticated users of security systems, choose passwords that are relatively insecure. As such, many password systems are easily accessed through a simple trial and error process.
A security access system that provides substantially secure access and does not require a password or access code is a biometric identification system. A biometric identification system accepts unique biometric information from a user and identifies the user by matching the information against information belonging to registered users of the system. One such biometric identification system is a fingerprint recognition system.
In a fingerprint input transducer or sensor, the finger under investigation is usually pressed against a flat surface, such as a side of a glass plate; the ridge and valley pattern of the finger tip is sensed by a sensing means such as an interrogating light beam.
Various optical devices are known which employ prisms upon which a finger whose print is to be identified is placed. The prism has a first surface upon which a finger is placed, a second surface disposed at an acute angle to the first surface through which the fingerprint is viewed and a third illumination surface through which light is directed into the prism. In some cases, the illumination surface is at an acute angle to the first surface, as seen for example, in U.S. Pat. Nos. 5,187,482 and 5,187,748. In other cases, the illumination surface is parallel to the first surface, as seen for example, in U.S. Pat. Nos. 5,109,427 and 5,233,404. Fingerprint identification devices of this nature are generally used to control the building-access or information-access of individuals to buildings, rooms, and devices such as computer terminals.
U.S. Pat. No. 4,353,056 in the name of Tsikos issued Oct. 5, 1982, discloses an alternative kind of fingerprint sensor that uses a capacitive sensing approach. The described sensor has a two dimensional, row and column, array of capacitors, each comprising a pair of spaced electrodes, carried in a sensing member and covered by an insulating film. The sensors rely upon deformation to the sensing member caused by a finger being placed thereon so as to vary locally the spacing between capacitor electrodes, according to the ridge/trough pattern of the fingerprint, and hence, the capacitance of the capacitors. In one arrangement, the capacitors of each column are connected in series with the columns of capacitors connected in parallel and a voltage is applied across the columns. In another arrangement, a voltage is applied to each individual capacitor in the array.
Sensing in the respective two arrangements is accomplished by detecting the change of voltage distribution in the series connected capacitors or by measuring the voltage values of the individual capacitances resulting from local deformation. To achieve this, an individual connection is required from the detection circuit to each capacitor.
Before the advent of computers and imaging devices, research was conducted into fingerprint characterisation and identification. Today, much of the research focus in biometrics has been directed toward improving the input transducer and the quality of the biometric input data. A second important issue to be addressed is the identification process itself and more particularly, the registration process.
A common method of registering users for a biometric identification system is to capture biometric input information, characterise it, and store it as a template. The same user then provides biometric input information to the system for identification. This is repeated several times and if identification is successful, the user and their biometric template are registered. Further, the system requires an experienced operator to accept or reject instances of biometric information intended as templates.
A further method of registering users for a biometric identification system is to capture a plurality of instances of biometric input information from a same user and to characterise each instance. A composite biometric template is then constructed in dependence upon the plurality of instances provided. Such a system is complicated and it requires an experienced operator to accept or reject instances of biometric information intended for template construction.